Yet define "sensibly" before we know what we're going to do with the infrastructure that results? The railways really started as a way to get coal to people (it's one of the defining characteristics of the English railways boom, that delivered coal prices slumped along each newly completed line) but much to the capitalists' surprise they really made their money by providing cheap transport to the working man. The railways were the reason for the invention of the day trip and commuting. Before the building of the lines, no one had any clue that this was where the money was going to be. Indeed, it took some of them a couple of decades (and a bankruptcy or two) before they got it.

Global Crossing was a disaster for anyone who put money into it and held on: yet the growth of things like YouTube (for whatever benefit that might have, little perhaps) was in part based upon all those thousands of miles of dark or light but hardly used fibre that had been laid in that orgy of let's piss away the shareholders' money.

And that's the little secret about infrastructure that is so little understood. It is not true that having infrastructure makes us or the society richer. It is rather that using it does. And we usually don't know how to use it until someone has gone and built a lot of it, people do that curious shaved monkey thing of experimenting with it and then we all find out. This is true of most inventions: it has been said that the biggest social change that the Model T brought was that women were less likely to be virgins at marriage. People worked out what to use the back seats for pretty quickly. The bicycle has been called the greatest contribution to the health of the working classes ever: it allowed courting outside the home village for the first time (amazing how inventions and sex seem to go together, eh? The first social network, Friends Reunited, is said to have caused a bubble in the divorce rate) to the benefit of the next generations' genes.

So these bubbles, they're not all bad. They provide an excess of whatever it is, which we then play with until we've worked out what to do with it. What we do with it is what allows the advance in wealth, even if those who built it for us have gone bust.

Back to Facebook though, and those projections of its future worth. One story says that in the rich world Facebook's number-growth has stopped, even gone into reverse. Hot growth stocks that aren't growing tend to be valued, as ex-hot growth stocks, not all that highly. And there's even a law change possible in the US that means that Facebook won't have to go public at all.

All of which means that not only do I not know what Facebook will be worth at IPO, I don't even know whether there will be a Facebook IPO. Which is exactly what your stockbroker will tell you (only more expensively). ®

* My own complaint about Groupon is that they refuse to sell my cheap golf coupons but that's another matter.